_DEBUG vs. NDEBUG: Which Preprocessor Define Should I Use for Debugging?

Debugging with _DEBUG and NDEBUG

When writing code that requires debugging, one must consider the appropriate preprocessor defines to use. Commonly, developers have a dilemma between using #ifdef _DEBUG, #ifndef NDEBUG, or defining a custom macro like #define MY_DEBUG.

_DEBUG vs NDEBUG: A Comparison

_DEBUG and NDEBUG serve distinct purposes: _DEBUG, specific to Visual Studio, is activated with the /MTd or /MDd compiler options. On the other hand, NDEBUG disables assertions defined by the C standard. It is crucial to use these defines appropriately. For instance, _DEBUG aligns debugging code with techniques employed by the Microsoft C Runtime library. Similarly, NDEBUG aligns with the behavior of the assert() function.

Alternative Approaches

If one prefers to define their custom debugging macros, it is advisable to avoid using names starting with an underscore. This naming convention is reserved by compilers and runtime environments.

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